Valve is setting loose a fresh batch of downloadable content for Left 4 Dead in September.

The DLC, dubbed Crash Course, is set for both the Xbox 360 and PC. Valve is promising new single-player, multiplayer and co-op content.

The official skinny goes like this: "...Crash Course bridges the gap between the end of the No Mercy campaign and the beginning of Death Toll in the original game, expanding the game universe with new locations, new dialogue from the original cast, and an explosive finale

"While containing both Survival maps and a Co-operative Campaign, the primary goal of Crash is to deliver a complete Versus mode experience in just 30 minutes, resulting in a streamlined version of the game's existing Versus campaigns. A recharge timer for infected teammates has also been added, and item spawn behavior has changed for more balanced gameplay."